HABITABILITY INFLUENCES BIOSIGNATURES IN MARS ANALOG LAVA TUBES

The National Academies Astrobiology Strategy (2019) prioritized subsurface exploration of Mars for evidence of habitability and extant or past life. Before we can effectively investigate the Mars’ subsurface, we must understand the distribution of life and biosignatures (indicators of life) in lava cave analogs on Earth. We investigated microbial colonization, using scanning electron microscopy, and biosignatures, including ATP bioluminescence assays, at the Craters of the Moon National Monument (CROM). CROM is a valuable Mars analogue because its temperature, precipitation and basalt composition similarities. We examined three nearby caves which had different internal temperatures (T): Ice Lake (T 0-0.2^oC); Pond (T 0.6-6.0^oC), and Screaming Jaws of Death (SJD; T 4.8-16.9^oC).

As a modification of the buried slide technique, we incubated sterilized basalt chips for 6 mo. and 1 yr. to evaluate microbial colonization (using scanning electron microscopy) and activity (ATP bioluminescence assay) changed over time. ATP, a biosignature of extant life, was measured by swabbing the basalt chips using Hygenia Ultrasnap™ surface ATP swabs and then measuring in relative light units (RLU) using a Hygenia systemSure™ ATP bioluminescence meter. Both microbial population size and microbial activity were greatest in warmer caves. SJD has the highest activity 1.77 RLU cm^-2, followed by Pond 0.68 RLU cm^-2, and Ice Lake 0.31 RLU cm^-2.

Microbial colonization and activity noticeably increased between 6 mo. and 1 yr. for all caves. SJD activity increased 523%, Pond 697%, and Ice Lake 404%. This suggests the duration of habitable conditions influences the detectability of extant biosignatures in lava tubes.